Quantricks is an online notebook for quantitative aptitude problems. You might like to use it as a ready-reckoner while solving those puzzling questions from competitve exams.
The website is organized into sections, and each section has some choicest types of questions, representative of commonly asked questions from recent exams like RBI grade B, SBI PO/ assistant, SSC CGL etc. Solutions are provided in a concise way. In case you need more examples of similar problems, or more detailed explanations, you might find some helpful links along with the notes.